This invention relates to a method for the determination of the density distribution of gas phase constituents in a plasma. The term "plasma" as employed in the instant application means an ionized gas which contains equal numbers of ions and electrons.
In particular the invention relates to a method for the determination of the density distribution of gas phase constituents of a plasma existing in an operating discharge lamp.
The method of the invention is particularly useful for the determination of the density distribution of mercury (H.sub.3) present in the plasma of an operating high pressure metal vapor discharge lamp.
The determination of the density distribution of the gas phase species in a plasma is important in understanding the chemistry of the plasma and thereby enhances the ability to improve the quality of the plasma.
Also, in many types of plasmas present in high density discharge lamps, the temperature distribution in such plasmas may be readily determined from its density distribution by the use of the gas laws. Knowledge of the temperature distribution in a plasma is also highly useful in understanding the chemistry of the plasma.
The density distribution of species in the plasma existing in an operating discharge lamp particularly a high pressure metal vapor discharge lamp, affects its efficacy, color rendition and useful life.
Thus, knowledge of the density distribution of the species present in a discharge lamp plasma is a key to the optimization of the design of the lamp. Additionally, the temperature distribution of the plasma which critically affects the operation of the lamp, may also readily be determined from the density distribution by employing the gas laws.
Attempts have been made to measure the temperature distribution in the plasma in a discharge lamp by means of optical methods.
These methods, such as described in H.S. Rothwell, Jr. et al J. IES Oct. 1980, pp. 40-46 and J. F. Waymouth, Electric Discharge Lamps, First Edition, M.I.T. Press, Cambridge, Mass., 1978, pp. 155 and 160-165 rely on an analysis of the emission spectra produced by operating lamps. These methods suffer from the defects of being undesirably slow and of being based on an assumption (among others) that the plasma in the operating lamp is axially symmetric. However, this assumption is not correct when the lamp is operated in a horizontal position.
In addition, by use of optical means it is not possible to obtain the temperature of the plasma near the wall of the plasma-containing tube but only in the luminous region of the arc.